Kiriakos,
1) A mid drive system takes advantage of the bikes gear system, which can allow the motor to run in it's most energy efficient rpm range, keeping amperage draw even, allowing smaller batteries to be used.
2) Rolling resistance is linear with speed, but wind resistance goes up exponentially, and wind resistance depends on the bike geometry so hard to say how much power your bike will require for a given speed. IIRC an average upright 1.25" tire bike uses about 125 watts at 15mph on flat ground, but hills require far more power or lower speed to keep current consumption even.
You need to look at the motor's power vs. heat curves to make a valid choice. I did try a hub drive bike, while it was impressive on flat land, I think it would have problems with long hills.
I overstated the speed of my electric moped, 46mph was downhill, about 35mph is the maximum for short distance without popping the 50amp breaker and/or overheating the motor, 25 MPH requires about 600 watts, the rated motor power for continuous operation. A fully faired recumbent bike could probably do 25mph with less than 150watts.
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You have move the electric bike concept in to a higher level. 
But lets go back to the humble bicycle and the electric assistance.
Some how I am getting more and more close to Mid-drive as main selection.
While I can imagine that performance and noise could be an small issue in direct comparison with a hub motor at flat road, what I liked more is the idea that Mid-drive motor when is out of use none of it mechanical parts are in motion, which translates to zero damage of it moving parts.
In my case, my home is 1.5km (1 mile) soft uphill and to return back to my workplace is the same distance as downhill , I am not pedaling at all.
When I need to buy electronics spare parts and I need to go down to the city center, it is also another mile which the mid-drive will help only in my return to base.
For what I am 100% convinced to use is the latest Headway 30120S cells.
Their fine print indicates that at 8 Ah max discharge current, I am up to their long life cycle specifications for 2000 recharge cycles or 5-7 years.
This 250W 36V mid-drive can do max 7A.
But lets go back to the humble bicycle and the electric assistance.
Some how I am getting more and more close to Mid-drive as main selection.
While I can imagine that performance and noise could be an small issue in direct comparison with a hub motor at flat road, what I liked more is the idea that Mid-drive motor when is out of use none of it mechanical parts are in motion, which translates to zero damage of it moving parts.
In my case, my home is 1.5km (1 mile) soft uphill and to return back to my workplace is the same distance as downhill , I am not pedaling at all.
When I need to buy electronics spare parts and I need to go down to the city center, it is also another mile which the mid-drive will help only in my return to base.
For what I am 100% convinced to use is the latest Headway 30120S cells.
Their fine print indicates that at 8 Ah max discharge current, I am up to their long life cycle specifications for 2000 recharge cycles or 5-7 years.
This 250W 36V mid-drive can do max 7A.
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Just found at very fresh topic which confirms my fears that a Mid drive system cannot keep up for long at max speed.
The link below is a story confirming that with 35Km on the speedometer the motor started smelling.
The rider had to maintain an 14.48 km/h speed so the motor to keep running with out getting damaged.
Endless-sphere.com • View topic - Super hiryuu - A Bafang BBS02 Dual sus bike that does it all
The link below is a story confirming that with 35Km on the speedometer the motor started smelling.
The rider had to maintain an 14.48 km/h speed so the motor to keep running with out getting damaged.
Endless-sphere.com • View topic - Super hiryuu - A Bafang BBS02 Dual sus bike that does it all
If the rider was using a hub motor, he would not have had the possibility of gearing down to 9mph, he would have had to back off the throttle and watch the motor suck electricity at a faster rate due to it operating at a less efficient rpm.
On a grade, in addition to rolling and wind resistance, the motor has to lift the weight of the bike and rider up the hill, in the case above the motor was able to provide 3668 feet of elevation at 9mph.
Unless you and your bike are lighter than that rider, you would need more than 60% more power than the above mentioned motor to maintain 35km/h up sustained 5-7% grades.
A motor built for mountains must be much more powerful than one used in a flat area, which is why I use one capable of a sustained 600 watts.
I do understand your point of view.
Unfortunately for every common mortal even at the range of 250 - 350W the major problem is the pricing even of the cheapest Mid-Drive motor that is commercially available.
By vendors as BAFANG and tjbewo, their products has a retail price in China at the range of 300$ USD, suddenly when these products traveling overseas their price raise 250% more.
The cause could be sellers acting as thieves and also express shipping companies cartel which both trying to take advantage of the stupid Europeans and Americans.
From the other hand one 250-1000W hub motor kit with all electronics, retails at 126$ USD.
The entire market place of electric bicycle KIT looks as slaughterhouse specially organized for lightweight thinking west guys that is supposed that carrying fat wallets.
The same story is happening with Lithium batteries, the best 15Ah 48V pack with BMC and carrying rack is around 320$.
Generally speaking if you do research this market thoroughly, and if you are a wise person, eventually you will be discouraged and you will back-of from the idea of getting an electrical KIT.
Last but not least, the part of service and maintenance, BAFANG Mid-Drive motor has lots of mechanical parts that will fail eventually, and there is only one place in China that seems to have the complete range.
I did requested from tjbewo - BEWO a blow-up diagram and parts list from their motor, and they avoiding doing so.
By my opinion if the ticket for a motor and batteries is around to 1000$ USD ( in the exit of the slaughterhouse) and there is no warranty for a healthy operation under normal conditions of 8 years, then this ticket is not worth it price.
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